Synthetic resin-made thrust sliding bearing

ABSTRACT

A synthetic resin-made thrust sliding bearing  1  includes a synthetic resin-made upper casing  100 , a synthetic resin-made lower casing  200 , and a synthetic resin-made thrust bearing piece  300  interposed between the upper and lower casings  100  and  200 . If it is assumed that the radial length of the thrust bearing piece  300  up to its outer peripheral surface  303  is (r), and the thickness of an upper annular plate portion  102  at its inner peripheral surface is (t), the upper casing  100  has on its upper surface  108  an annular flat surface  109  having a circular outer peripheral edge with R in a range of R=r±t.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. application Ser. No.13/056,407, filed Feb. 9, 2001, now U.S. Pat. No. 9,188,153, which isthe U.S. National Phase of International Application No.PCT/JP2009/003465, filed Jul. 23, 2009, which designated the U.S andclaims priority to Japanese Patent Application no. 2008-194078, filedJul. 28, 2008, the entire contents of each of which are herebyincorporated by reference.

TECHNICAL FIELD

The present invention relates particularly to a synthetic resin-madethrust sliding bearing which is suitably incorporated as a thrustsliding bearing of a strut-type suspension (Macpherson type) in afour-wheeled motor vehicle.

BACKGROUND ART

In general, a strut-type suspension is mainly used in a front wheel of afour-wheeled motor vehicle, and is constructed such that a strutassembly incorporating a hydraulic shock absorber in an outer cylinderformed integrally with a main shaft is combined with a coil spring.Among such suspensions, there is a type of structure in which the axisof the coil spring is actively offset with respect to the axis of thestrut, so as to allow the sliding of a piston rod of the shock absorberincorporated in the strut to be effected smoothly. There is another typeof structure in which the coil spring is disposed by aligning the axisof the coil spring with the axis of the strut. In either structure, abearing is disposed between a mounting member for a motor vehicle bodyand an upper spring seat of the coil spring to allow the rotation to beeffected smoothly when the strut assembly rotates together with the coilspring by the steering operation.

In this thrust bearing, a rolling bearing using balls or needles or asynthetic resin-made sliding bearing is used. However, the rollingbearing has a possibility of causing a fatigue failure in the balls orneedles owing to such as infinitesimal oscillations and a vibratoryload, so that there is a problem in that it is difficult to maintain asmooth steering operation. As compared with the rolling bearing, thethrust sliding bearing has a high frictional torque and therefore hasthe problem that the steering operation is made heavy. Furthermore, bothbearings have the problem that the steering operation is made heavy dueto the high frictional force of a dust seal formed of a rubber elastomerfitted to prevent the ingress of foreign objects such as dust ontosliding surfaces, and the synthetic resin-made sliding bearing inparticular has the problem that the steering operation is made muchheavier.

To overcome the above-described problems, the present applicant proposedsynthetic resin-made thrust sliding bearings which are each comprised ofa synthetic resin-made upper casing, a synthetic resin-made lowercasing, and a synthetic resin-made bearing piece interposed between theupper and lower casings, wherein the upper and lower casings arecombined by elastic fitting, and a resiliently fitting portion and asealing portion based on labyrinth action are respectively formedbetween the upper and lower casings and between an inner peripheralsurface side and an outer peripheral surface side, to prevent the entryof foreign objects such as dust onto the bearing sliding surface bymeans of that sealing portion (described in Patent Document 1, PatentDocument 2, Patent Document 3, Patent Document 4, and Patent Document5).

This thrust bearing will be described with reference to drawings asfollows. In FIGS. 12 and 13, a synthetic resin-made thrust slidingbearing 1 is disposed between a vehicle body-side mounting member Xfixed to the vehicle body side by means of a mount insulator and a flatupper surface Q1 of an upper spring seat Q disposed in such a manner asto oppose a lower surface X1 of the vehicle body-side mounting member Xand surround an outer peripheral surface P1 of a piston rod P fixed atits one end to the vehicle body-side mounting member X. This syntheticresin-made thrust sliding bearing 1 is comprised of a syntheticresin-made upper casing 100, a synthetic resin-made lower casing 200,and a synthetic resin-made bearing piece 30 interposed between the upperand lower casings 10 and 20. The upper casing 10 includes: an annularplate portion 12 having a circular hole 11 in its central portion, acylindrical suspended portion 14 formed integrally with a lower surface13 of the annular plate portion 12 in such a manner as to be radiallyoutwardly spaced apart a predetermined interval from a peripheral edgeof the circular hole 11; a cylindrical engaging suspended portion 16formed integrally at an outer peripheral edge of the annular plateportion 12 in such a manner as to be radially outwardly spaced apart apredetermined interval from the cylindrical suspended portion 14, so asto form an annular groove 15 in cooperation with the cylindricalsuspended portion 14; and an engaging hook portion 17 formed on an innerperipheral surface of an end portion of the cylindrical engagingsuspended portion 16. The lower casing 20 includes: an annular plateportion 22 having in a central portion thereof an insertion hole 21communicating with the circular hole 11 of the upper casing 10; anannular projection 23 having an inside diameter identical to that of theinsertion hole 21 and formed integrally on an upper surface of theannular plate portion 22; an annular projection 25 formed integrally onthe upper surface of the annular plate portion 22 in such a manner as tobe radially outwardly spaced apart a predetermined interval from theannular projection 23, so as to form an annular recess 24 in cooperationwith the annular projection 23 and the upper surface of the annularplate portion 22; a cylindrical engaging projecting portion 27 formedintegrally at an outer peripheral edge of the annular plate portion 22in such a manner as to be radially outwardly spaced apart apredetermined interval from the annular projection 25, so as to form anannular groove 26 in cooperation with the annular projection 25; anengaged portion 28 formed on an outer peripheral surface of thecylindrical engaging projecting portion 27; and a cylindrical portion 29having an inside diameter identical to that of the insertion hole 21 andformed integrally on the lower surface of the lower casing 20. The uppercasing 10 is combined with the lower casing 20 by causing the engaginghook portion 17 to be resiliently fitted to the engaged portion 28 ofthe lower casing 20.

PRIOR ART DOCUMENTS Patent Documents

[Patent Document 1] JP-UM-B-4-52488

[Patent Document 2] JP-UM-B-2-1532

[Patent Document 3] JP-UM-B-2-6263

[Patent Document 4] JP-UM-B-8-2500

[Patent Document 5] JP-UM-B-4-47445

SUMMARY OF THE INVENTION Problems that the Invention is to Solve

With the synthetic resin-made thrust sliding bearing, it is possible toovercome the problem of an increase in the steering operating forcecaused by the dust seal formed of a rubber elastomer fitted between thesliding surfaces in such a manner as to surround the sliding surfaces,and it is possible to obtain a stable and smooth steering operatingforce by preventing as practically as possible the entry of foreignobjects such as dust onto the sliding surfaces.

As for the synthetic resin-made thrust sliding bearing 1 disposedbetween the vehicle body-side mounting member X and the upper surface Q1of the upper spring seat Q, in a case where a fluctuating load such asan inclination has acted on the vehicle body-side mounting member X,interference occurs at radially superposed portions of the cylindricalengaging suspended portion 14 of the upper casing 10 and the annularprojection 25 and the cylindrical engaging projecting portion 27 of thelower casing 20, as well as at resiliently fitting portions of theengaging hook portion 17 of the cylindrical engaging suspended portion16 of the upper casing 10 and the engaged portion 28 of the cylindricalengaging projecting portion 27 of the lower casing 20. As a result,problems occurred such as the deformation, damage, and breakage of theengaging portions. Further, problems were found in that as an excessiveload is applied to the bearing piece 30 of the synthetic resin-madethrust sliding bearing 1 disposed between the upper and lower casings 10and 20, a creep (cold flow) phenomenon is induced in the bearing piece30, and a shift due to creep deformation of that bearing piece 30 takesplace from original sliding through the bearing piece 30 to slidingbetween the upper and lower casings 10 and 20, causing a decline in thesliding characteristics such as an increase in the coefficient offriction and the deterioration of wear resistance.

As a result of conducting strenuous studies to overcome theabove-described problems, it was found that even in the case where afluctuating load such as an inclination has acted on the vehiclebody-side mounting member X, the above-described problems can beovercome by specifying the position of contact of the upper surface ofthe upper casing of the synthetic resin-made thrust sliding bearing incontact with the lower surface of the vehicle body-side mounting memberbetween the vehicle body-side mounting member and the upper spring seatbetween which the synthetic resin-made thrust sliding bearing isdisposed, without causing interference at the superposed portions of thecylindrical engaging suspended portion 14 of the upper casing 10 and theannular projection 25 and the cylindrical engaging projecting portion 27of the lower casing 20 and at resiliently fitting portions of theengaging hook portion 17 of the cylindrical engaging suspended portion16 of the upper casing 10 and the engaged portion 28 of the cylindricalengaging projecting portion 27 of the lower casing 20. Further, it wasfound that even in the case where creep deformation has occurred in thebearing piece 30, it is possible to constantly allow sliding to beeffected through the thrust bearing piece without undergoing a shift tosliding between the upper and lower casings 10 and 20, thereby making itpossible to maintain the sliding characteristics such as low frictioncharacteristics and wear resistance for extended periods of time.

The present invention has been devised on the basis of theabove-described finding, and its object is to provide a syntheticresin-made thrust sliding bearing which is comprised of syntheticresin-made upper and lower casings and a synthetic resin-made thrustsliding bearing piece interposed between the upper and lower casings,and which, even in cases where a fluctuating load such as an inclinationhas acted on the vehicle body-side mounting member, permits smoothsteering operation without causing interference between the upper casingand the lower casing, which would otherwise cause problems such as thedeformation, damage, and breakage of the engaging portions, or whichwould apply an excessive load on the sliding bearing piece interposedbetween the upper and lower casings and cause plastic deformationthereof.

Means for Overcoming the Problems

A synthetic resin-made thrust sliding bearing in accordance with thepresent invention comprises: a synthetic resin-made upper casingincluding an upper annular plate portion having a circular hole in itscentral portion, a first cylindrical suspended portion formed integrallyon a lower surface of the upper annular plate portion in such a manneras to be radially outwardly spaced apart a predetermined interval froman inner peripheral surface of the upper annular plate portion definingthe circular hole, a cylindrical engaging suspended portion formedintegrally on the lower surface of the upper annular plate portion at anouter peripheral edge thereof in such a manner as to be radiallyoutwardly spaced apart a predetermined interval from the firstcylindrical suspended portion, so as to form an upper outer annulargroove in cooperation with the first cylindrical suspended portion, andan annular engaging portion formed on an inner peripheral surface of thecylindrical engaging suspended portion; a synthetic resin-made lowercasing including a lower annular plate portion having in its centralportion an insertion hole concentric with the circular hole of the upperannular plate portion, a first annular projection formed integrally onan upper surface of the lower annular plate portion on an innerperipheral side thereof, a second annular projection formed integrallyon the upper surface of the lower annular plate portion in such a manneras to be radially outwardly spaced apart a predetermined interval fromthe first annular projection, so as to form at its inner peripheralsurface a lower annular recess in cooperation with an outer peripheralsurface of the first annular projection and the upper surface of thelower annular plate portion, a cylindrical engaging projecting portionformed integrally on the upper surface of the lower annular plateportion at the outer peripheral edge thereof in such a manner as to beradially outwardly spaced apart a predetermined interval from the secondannular projection, so as to form at its inner peripheral surface alower outer annular groove in cooperation with an outer peripheralsurface of the second annular projection, and an annular engaged portionformed on an outer peripheral surface of the cylindrical engagingprojecting portion; and a thrust bearing piece formed in a form of asynthetic resin-made annular disk, disposed in the lower annular recess,and having a circular hole in a central portion thereof, wherein thethrust bearing piece is disposed in the lower annular recess whilemaintaining an inner annular clearance between its inner peripheralsurface defining the circular hole and an outer peripheral surface ofthe first annular projection and maintaining an outer annular clearancebetween its outer peripheral surface and an inner peripheral surface ofthe second annular projection, respectively, the thrust bearing piecebeing disposed in the lower annular recess such that its upper surfaceis positioned between an opening plane of the lower annular recess andthe lower surface of the upper annular plate portion by being broughtinto sliding contact with the lower surface of the upper annular plateportion, and such that its lower surface is positioned by being broughtinto sliding contact with the upper surface of the lower annular plateportion defining a bottom surface of the lower annular recess, andwherein the upper casing is combined with the lower casing by disposingthe first cylindrical suspended portion in the lower outer annulargroove so as to be radially superposed on the second annular projectionand the cylindrical engaging projecting portion, and by causing theengaging portion to be resiliently fitted to the engaged portion, thesynthetic resin-made thrust sliding bearing characterized in that if itis assumed that a radial length from an axis of the upper casing to theouter peripheral surface of the thrust bearing piece disposed in thelower annular recess is (r), and a thickness of the upper annular plateportion at its inner peripheral surface is (t), the upper casing has onits upper surface an annular flat surface having a circular outerperipheral edge whose radius (R) with the axis of the upper casing setas a center is in a range of R=r±t, and that the synthetic resin-madethrust sliding bearing is disposed between a lower surface of a vehiclebody-side mounting member and an upper surface of an upper spring seatopposing that lower surface, such that only the annular flat surface isbrought into contact with the lower surface of the vehicle body-sidemounting member.

According to the present invention, the upper casing has on its uppersurface an annular flat surface which satisfies the above-describedrelational formula, and the synthetic resin-made thrust sliding bearingis disposed between the lower surface of a vehicle body-side mountingmember and the upper surface of an upper spring seat, such that only theannular flat surface is brought into contact with the lower surface ofthe vehicle body-side mounting member, while, at its other portions,maintaining a space with respect to the lower surface of the vehiclebody-side mounting member. Therefore, even in the case where afluctuating load such as an inclination has acted on the vehiclebody-side mounting member, interference does not occur at radiallysuperposed portions of the first cylindrical suspended portion of theupper casing and the second annular projection and the cylindricalengaging projecting portion of the lower casing, as well as atresiliently fitting portions of the engaging portion of the cylindricalengaging suspended portion of the upper casing and the engaged portionof the cylindrical engaging projecting portion of the lower casing.Hence, problems such as the deformation, damage, breakage, and the likedo not occur in these superposed portions and resiliently fittingportions.

In the annular flat surface having a circular outer peripheral edge of alength smaller than the length of R=r−t in the above described formula,an excessive load would be applied to the thrust bearing piece in thesynthetic resin-made thrust sliding bearing, and would cause creep andthe like in the thrust bearing piece, resulting in a decline in lowfriction characteristics and wear resistance. On the other hand, in theannular flat surface having a circular outer peripheral edge of a lengthgreater than the length of R=r+t, in the case where a fluctuating loadsuch as an inclination has acted on the vehicle body-side mountingmember, interference can possibly occur at the radially superposedportions of the first cylindrical suspended portion of the upper casingand the second annular projection and the cylindrical engagingprojecting portion of the lower casing, as well as at the resilientlyfitting portions of the engaging portion of the cylindrical engagingsuspended portion of the upper casing and the engaged portion of thecylindrical engaging projecting portion of the lower casing. Hence,problems such as the deformation, damage, breakage, and the like canpossibly occur in these superposed portions and resiliently fittingportions. Accordingly, the annular flat surface which is formed on theupper surface of the upper casing has a circular outer peripheral edgeof a length whose radius (R) with the axis of the upper casing set as acenter is in a range of R=r±t, preferably a circular outer peripheraledge of a length whose radius (R) is R=r.

In addition, according to the synthetic resin-made thrust slidingbearing in accordance with the above-described aspect, the upper casingis combined with the lower casing by disposing the first cylindricalsuspended portion in the lower outer annular groove so as to be radiallysuperposed on the second annular projection and the cylindrical engagingprojecting portion, and by causing the engaging portion to beresiliently fitted to the engaged portion. Therefore, sealed portionsbased on the labyrinth action are formed at the radially superposedportions of the first cylindrical suspended portion and the secondannular projection and the cylindrical engaging projecting portion andat the resiliently fitting portions of the engaging portion and theengaged portion, with the result that an operational effect is furtheradded in that the entry of foreign objects such as dust between theupper and lower casings can be prevented.

In the synthetic resin-made thrust sliding bearing in accordance withthe present invention, the annular flat surface may be constituted by anupper surface of the upper annular plate portion. However, in a casewhere the upper casing further has an annular projecting portionprojecting in an axial direction integrally from the upper surface ofthe upper annular plate portion, the annular flat surface may beconstituted by the upper surface of the annular projecting portion.Further, the upper casing may have on its upper surface a truncatedconical surface with a descending gradient extending from an outerperipheral edge of the annular flat surface or from a radially outerportion of that outer peripheral edge to its outer peripheral surface.

According to the synthetic resin-made thrust sliding bearing inaccordance with the above-described aspects, it is possible to morereliably avoid the interference at the radially superposed portions ofthe first cylindrical suspended portion of the upper casing and thesecond annular projection and the cylindrical engaging projectingportion of the lower casing and at the resiliently fitting portions ofthe engaging portion of the cylindrical engaging suspended portion ofthe upper casing and the engaged portion of the cylindrical engagingprojecting portion of the lower casing in the case where a fluctuatingload such as an inclination has acted on the vehicle body-side mountingmember.

In the synthetic resin-made thrust sliding bearing in accordance withthe present invention, the upper casing may further have a secondcylindrical suspended portion which is radially outwardly adjacent tothe circular hole in the central portion of the upper annular plateportion via an annular shoulder portion, and is formed integrally on thelower surface of the upper annular plate portion in such a manner as tobe radially inwardly spaced apart a predetermined interval from an innerperipheral surface of the first cylindrical suspended portion, so as toform at its outer peripheral surface an upper annular recess incooperation with the inner peripheral surface of the first cylindricalsuspended portion and the lower surface of the upper annular plateportion. Additionally, the lower casing may further have a third annularprojection which has an inside diameter identical to that of theinsertion hole formed in the central portion of the lower annular plateportion and is formed integrally on the upper surface of the lowerannular plate portion in such a manner as to be radially inwardly spacedapart a predetermined interval from the first annular projection, so asto form at its outer peripheral surface a lower inner annular groove incooperation with the inner peripheral surface of the first annularprojection. In such an upper casing and a lower casing, the upper casingmay be combined with the lower casing by disposing the secondcylindrical suspended portion in the lower inner annular groove so as tobe radially superposed on the first annular projection and the thirdannular projection.

According to the synthetic resin-made thrust sliding bearing inaccordance with the above-described aspects, since the upper casing iscombined with the lower casing by disposing the second cylindricalsuspended portion in the lower inner annular groove so as to be radiallysuperposed on the first annular projection and the third annularprojection, sealed portions based on the labyrinth action are furtherformed at the radially superposed portions of the second cylindricalsuspended portion and the first annular projection and the third annularprojection. As a result, an operational effect is added in that theentry of foreign objects such as dust between the upper and lowercasings, particularly from the inner peripheral surface side of theupper and lower casings, can be further prevented.

In the synthetic resin-made thrust sliding bearing in accordance withthe present invention, the upper casing may further have a secondcylindrical suspended portion which has an inside diameter identical tothat of the insertion hole in the central portion of the upper annularplate portion and is formed integrally on the lower surface of the upperannular plate portion and a third cylindrical suspended portion formedintegrally on the lower surface of the upper annular plate portion insuch a manner as to be radially outwardly spaced apart a predeterminedinterval from an outer peripheral surface of the second cylindricalsuspended portion, so as to form at its inner peripheral surface anupper inner annular groove in cooperation with the outer peripheralsurface of the second cylindrical suspended portion. Additionally, thelower casing may further have a third annular projection which is formedintegrally on the upper surface of the lower annular plate portion insuch a manner as to be radially outwardly spaced apart from theinsertion hole in the central portion of the lower annular plate portionvia an annular shoulder portion, and is disposed in such a manner as tobe radially inwardly spaced apart a predetermined interval from theinner peripheral surface of the first annular projection, so as to format its outer peripheral surface a lower inner annular groove incooperation with the inner peripheral surface of the first annularprojection. In such an upper casing and a lower casing, the upper casingmay be combined with the lower casing by radially superposing the secondcylindrical suspended portion on the third annular projection, bydisposing the third annular projection in the upper inner annulargroove, and by disposing the third cylindrical suspended portion in thelower inner annular groove so as to be radially superposed on the firstannular projection and the third annular projection, respectively.

According to the synthetic resin-made thrust sliding bearing inaccordance with the above-described aspect, since the upper casing iscombined with the lower casing by radially superposing the secondcylindrical suspended portion on the third annular projection, bydisposing the third annular projection in the upper inner annulargroove, and by disposing the third cylindrical suspended portion in thelower inner annular groove so as to be radially superposed on the firstannular projection and the third annular projection, respectively,sealed portions based on the labyrinth action are formed at the radiallysuperposed portions of the second and third cylindrical suspendedportions, on the one hand, and the first annular projection and thethird annular projection, on the other hand. As a result, an operationaleffect is added in that the entry of foreign objects such as dustbetween the upper and lower casings, particularly from the innerperipheral surface side of the upper and lower casings, can be furtherprevented.

In the synthetic resin-made thrust sliding bearing in accordance withthe above-described aspects, if it is assumed that a diameter of theouter peripheral surface of the first annular projection is (c), adiameter of the inner peripheral surface of the second annularprojection is (d), a diameter of the inner peripheral surface of thethrust sliding bearing piece is (a), a diameter of the outer peripheralsurface of the thrust sliding bearing piece is (b), a depth of the lowerannular recess corresponding to a distance from the bottom surface ofthe lower annular recess to the opening plane of the lower annularrecess is (f), and a thickness of the thrust bearing piece is (e), thena sum A of volumes of the inner annular clearance and the outer annularclearance and a volume B of that portion of the thrust bearing piecewhich projects from the opening plane of the lower annular recess may bein a relationship of B>A shown by a following formula:e(b ² −a ²)>f(d ² −c ²).

As the above-described relational formula is satisfied, an operationaleffect is added in that even in the case where creep deformation hasoccurred in the thrust bearing piece of the synthetic resin-made thrustsliding bearing interposed between the upper and lower casings, it ispossible to constantly allow sliding to be effected through the thrustbearing piece without undergoing a shift to sliding between the upperand lower casings, thereby making it possible to maintain the slidingcharacteristics such as low friction characteristics and wear resistancefor extended periods of time.

In the synthetic resin-made thrust sliding bearing in accordance withthe above-described aspects, the thrust bearing piece may have on eachof the upper and lower surfaces thereof an annular groove whichsurrounds the circular hole and a plurality of radial grooves eachhaving one end open at the annular groove and another end open at theouter peripheral surface and arranged in a circumferential direction.Further, the lower casing may have a cylindrical portion formedintegrally on the lower surface of the lower annular plate portion andhaving an inside diameter identical to that of the insertion hole.

According to the synthetic resin-made thrust sliding bearing which hasthe cylindrical portion formed integrally on the lower surface of thelower annular plate portion and having an inside diameter identical tothat of the insertion hole, the mounting of the synthetic resin-madethrust sliding bearing to the mounting member can be effected byinserting the cylindrical portion into a mounting hole formed in themounting member, so that the mounting operation can be highlysimplified.

Advantages of the Invention

According to the present invention, if it is assumed that the radiallength from the axis of the upper casing to the outer peripheral surfaceof the thrust bearing piece disposed in the lower annular recess is (r),and the thickness of the upper annular plate portion at its innerperipheral surface is (t), the upper casing has on its upper surface theannular flat surface having a circular outer peripheral edge whoseradius (R) with the axis of the upper casing set as a center is in arange of R=r±t, and the upper casing is disposed by being brought atonly its annular flat surface into contact with the lower surface of thevehicle body-side mounting member. Since the synthetic resin-made thrustsliding bearing having this upper casing is disposed between the lowersurface of the vehicle body-side mounting member and the upper surfaceof the upper spring seat, it is possible to provide a syntheticresin-made thrust sliding bearing in which, even in cases where afluctuating load such as an inclination has acted on the vehiclebody-side mounting member, interference does not occur at the radiallysuperposed portions of the cylindrical suspended portion of the uppercasing and the second annular projection and the cylindrical engagingprojecting portion of the lower casing and at the resiliently fittingportions of the engaging portion of the cylindrical engaging suspendedportion and the engaged portion of the cylindrical engaging projectingportion, thereby making it possible to prevent the occurrence ofproblems such as the deformation, damage, breakage, and the like inthese superposed portions and resiliently fitting portions.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of a preferred first embodiment of theinvention;

FIG. 2 is a plan view of a thrust bearing piece;

FIG. 3 is a plan view of an upper casing;

FIG. 4 is a cross-sectional view of a modification of the preferredfirst embodiment of the invention;

FIG. 5 is a cross-sectional view of another modification of thepreferred first embodiment of the invention;

FIG. 6 is an explanatory diagram of an example in which the embodimentshown in FIG. 1 is incorporated in a strut-type suspension;

FIG. 7 is an explanatory diagram explaining the relationship between alower casing and the thrust bearing piece in the embodiment of FIG. 1;

FIG. 8 is a cross-sectional view of a preferred second embodiment of theinvention;

FIG. 9 is a cross-sectional view of a preferred third embodiment of theinvention;

FIG. 10 is a cross-sectional view of a preferred fourth embodiment ofthe invention;

FIG. 11 is a cross-sectional view of a preferred fifth embodiment of theinvention;

FIG. 12 is a cross-sectional view of a conventional synthetic resin-madethrust sliding bearing; and

FIG. 13 is an explanatory diagram of an example in which the exampleshown in FIG. 12 is incorporated in the strut-type suspension.

MODE FOR CARRYING OUT THE INVENTION

Hereafter, a more detailed description will be given of the presentinvention with reference to preferred embodiments shown in the drawings.It should be noted that the present invention is not limited to theseembodiments.

In FIGS. 1 to 3, a synthetic resin-made thrust sliding bearing 1 inaccordance with a first embodiment of the invention is comprised of asynthetic resin-made upper casing 100, a synthetic resin-made lowercasing 200, and a synthetic resin-made thrust bearing piece 300interposed between the upper and lower casings 100 and 200.

The upper casing 100 includes an upper annular plate portion 102 havinga circular hole 101 in its central portion; a cylindrical suspendedportion 104 formed integrally on a lower surface 103 of the upperannular plate portion 102 in such a manner as to be radially outwardlyspaced apart a predetermined interval from an inner peripheral surfaceof the upper annular plate portion 102 defining the circular hole 101; acylindrical engaging suspended portion 106 formed integrally on thelower surface 103 of the upper annular plate portion 102 at an outerperipheral edge thereof in such a manner as to be radially outwardlyspaced apart a predetermined interval from the cylindrical suspendedportion 104, so as to form an upper outer annular groove 105 incooperation with the cylindrical suspended portion 104; and an engagingportion 107 formed on an inner peripheral surface of the cylindricalengaging suspended portion 106.

The lower casing 200 includes a lower annular plate portion 202 havingin its central portion an insertion hole 201 concentric with thecircular hole 101; an annular projection 204 having an inside diameteridentical to that of the insertion hole 201 and formed integrally on anupper surface 203 of the lower annular plate portion 202; an annularprojection 206 formed integrally on the upper surface 203 of the lowerannular plate portion 202 in such a manner as to be radially outwardlyspaced apart a predetermined interval from the annular projection 204,so as to form at its inner peripheral surface a lower annular recess 205in cooperation with an outer peripheral surface of the annularprojection 204 and the upper surface 203 of the lower annular plateportion 202; a cylindrical engaging projecting portion 208 formedintegrally on the upper surface 203 of the lower annular plate portion202 at an outer peripheral edge thereof in such a manner as to beradially outwardly spaced apart a predetermined interval from theannular projection 206, so as to form at its inner peripheral surface alower outer annular groove 207 in cooperation with an outer peripheralsurface of the annular projection 206; and an annular engaged portion209 formed on an outer peripheral surface of the cylindrical engagingprojecting portion 208.

The thrust bearing piece 300 is constituted by a disk 304 which has inits central portion a circular hole 302 defined by an inner peripheralsurface 301 having an inside diameter larger than the outside diameterof the outer peripheral surface of the annular projection 204 and has anouter peripheral surface 303 having an outside diameter smaller than theinside diameter of the annular projection 206. The thrust bearing piece300 is disposed in the lower annular recess 205 while maintaining aninner annular clearance A1 between the inner peripheral surface 301defining the circular hole 302 and an outer peripheral surface 210 ofthe annular projection 204 and maintaining an outer annular clearance A2between the outer peripheral surface 303 and an inner peripheral surface211 of the annular projection 206, respectively. Further, the thrustbearing piece 300 is disposed in the lower annular recess 205 such thatits upper surface 305 is positioned between an opening plane of thelower annular recess 205 of the lower casing 200 and the lower surface103 of the upper annular plate portion 102 by being brought into slidingcontact with the lower surface 103 of the upper annular plate portion102, and such that its lower surface 306 is positioned by being broughtinto sliding contact with the upper surface 203 of the lower annularplate portion 202 defining a bottom surface 212 of the lower annularrecess 205.

As shown in FIG. 2, the thrust bearing piece 300 has on each of itsupper and lower surfaces 305 and 306 an annular groove 307 whichsurrounds the circular hole 302, as well as a plurality of radialgrooves 308 each having one end open at the annular groove 307 and theother end open at the outer peripheral surface 303 and arranged at equalintervals in the circumferential direction. A lubricant such as greaseis filled in these annular grooves 307 and radial grooves 308.

The upper casing 100 is combined with the lower casing 200 by disposingan end portion of the cylindrical suspended portion 104 in the lowerouter annular groove 207 so as to be radially superposed on end portionsof the annular projection 206 and the cylindrical engaging projectingportion 208, and by causing the engaging portion 107 to be resilientlyfitted to the engaged portion 209.

With the synthetic resin-made thrust sliding bearing 1, if it is assumedthat the radial length from an axis (o) of the upper casing 100 to theouter peripheral surface 303 of the thrust bearing piece 300 disposed inthe lower annular recess 205 is (r), and that the thickness of the upperannular plate portion 102 at its inner peripheral surface is (t), theupper casing 100 has, on an upper surface 108 of the upper annular plateportion 102 constituting its upper surface, an annular flat surface 109having an outer peripheral edge whose radius (R) with the axis (o) ofthe upper casing 100 set as a center is in a range of R=r±t, as well asa truncated conical surface portion 111 with a descending gradientextending continuously from an outer peripheral edge of the annular flatsurface 109 or from a radially outer portion of that outer peripheraledge to its outer peripheral surface 110.

In this embodiment, as shown in FIG. 1, the upper casing 100 has, on theupper surface 108 of the upper annular plate portion 102 constitutingits upper surface, the annular flat surface 109 having an outerperipheral edge whose radius (R) with the axis (o) of the upper casing100 as a center is R=r. It should be noted that FIG. 4 shows an examplein which the annular flat surface 109 having an outer peripheral edgewhose radius (R) with the axis (o) of the upper casing 100 set as acenter is R=r−t is provided on the upper surface 108 of the upperannular plate portion 102, and FIG. 5 shows an example in which theannular flat surface 109 having an outer peripheral edge whose radius(R) with the axis (o) of the upper casing 100 set as a center is R=r+tis provided on the upper surface 108 of the upper annular plate portion102.

As shown in FIG. 6, the above-described synthetic resin-made thrustsliding bearing 1 is disposed between a lower surface X1 of a vehiclebody-side mounting member X and an upper surface Q1 of an upper springseat Q opposing that lower surface X1, such that only the annular flatsurface 109 of the upper surface 108 of the upper annular plate portion102 is brought into contact with the lower surface X1 of the vehiclebody-side mounting member X, while, at its other portions, maintaining aspace S with respect to the lower surface X1 of the vehicle body-sidemounting member X. Therefore, even in the case where a fluctuating loadsuch as an inclination has acted on the vehicle body-side mountingmember X, interference does not occur at radially superposed portions ofthe cylindrical suspended portion 104 and the annular projection 206 andthe cylindrical engaging projecting portion 208, as well as atresiliently fitting portions of the engaging portion 107 of thecylindrical engaging suspended portion 106 and the engaged portion 209of the cylindrical engaging projecting portion 208. Hence, problems suchas the deformation, damage, breakage, and the like do not occur in thesesuperposed portions and resiliently fitting portions.

With the above-described synthetic resin-made thrust sliding bearing 1,the upper casing 100 is combined with the lower casing 200 by disposingthe end portion of the cylindrical suspended portion 104 in the lowerouter annular groove 207 so as to be radially superposed on the endportions of the annular projection 206 and the cylindrical engagingprojecting portion 208, and by causing the engaging portion 107 to beresiliently fitted to the engaged portion 209. Therefore, sealedportions based on the labyrinth action are formed at the radiallysuperposed portions of the cylindrical suspended portion 104 and theannular projection 206 and the cylindrical engaging projecting portion208 and at the resiliently fitting portions of the engaging portion 107and the engaged portion 209, with the result that an operational effectis added in that the entry of foreign objects such as dust between theupper and lower casings 100 and 200 can be prevented.

With the synthetic resin-made thrust sliding bearing 1, as shown in FIG.7, if it is assumed that the diameter of the outer peripheral surface210 of the annular projection 204 is c, the diameter of the innerperipheral surface 211 of the annular projection 206 is d, the diameterof the inner peripheral surface 301 of the thrust bearing piece 300defining the circular hole 302 is a, the diameter of the outerperipheral surface 303 of the thrust bearing piece 300 is b, the depthof the lower annular recess 205 corresponding to the distance from thebottom surface of the lower annular recess 205 to the opening plane ofthe lower annular recess 205 is f, and the thickness of the thrustbearing piece 300 is e, then a sum A of volumes of the inner annularclearances A1 and A2 and a volume B of that portion of the thrustbearing piece 300 which projects upward from the opening plane of thelower annular recess 205 are preferably in a relationship of B>A, i.e.,e(b²−a²)>f(d²−c²) (refer to the below-described calculating formula).According to this arrangement, even in cases where a change (decrease)in the thickness due to creep deformation has occurred to the thrustbearing piece 300 in the lower annular recess 205, the change (decrease)in the thickness is restrained in the lower annular recess 205, and itsfurther change (decrease) in the thickness is prevented. Further, sincethe upper surface 305 of the thrust bearing piece 300 constantlyprojects from the opening plane of the lower annular recess 205 of thelower casing 200, the upper and lower casings 100 and 200 can constantlybe made to undergo sliding through the thrust bearing piece 300 withoutshifting to sliding between the upper and lower casings 100 and 200.Thus, an operational effect is added in that it is possible to maintainthe sliding characteristics such as low friction characteristics andwear resistance over extended periods of time.

[Mathematical Formula 1]

(Calculating Formula)Volume of inner annular clearance A1=(a ² −c ²)×π·f/4Volume of outer annular clearance A2=(d ² −b ²)×π·f/4Annular clearance A (A1+A2)=(a ² −c ² +d ² −b ²)×π·f/4

Volume B of the portion of the thrust bearing piece projecting upwardfrom the opening plane of the lower annular recessB=(b ² −a ²)×π·(e−f)/4  From B>A, we have e(b ² −a ²)>f(d ² −c ²).

As for the upper casing 100 and the lower casing 200, a thermoplasticsynthetic resin such as polyacetal resin, polyamide resin, and polyesterresin is suitably used. In addition, as the synthetic resin for formingthe thrust bearing piece 300, a thermoplastic synthetic resin such aspolyamide resin, polyolefin resin, and polyester resin, which excel inthe sliding characteristics with respect to the thermoplastic syntheticresin for forming the upper casing 100 and the lower casing 200, issuitably used.

FIG. 9 shows the synthetic resin-made thrust sliding bearing 1 inaccordance with a second embodiment, and this synthetic resin-madethrust sliding bearing 1 has, in addition to the construction of thesynthetic resin-made thrust sliding bearing 1 in accordance with thefirst embodiment, a cylindrical portion 214 which has an inside diameteridentical to that of the insertion hole 201 and is formed integrallywith a lower surface 213 of the lower annular plate portion 202.

With the synthetic resin-made thrust sliding bearing 1 having thecylindrical portion 214 on the lower surface 213 of the lower casing200, when it is installed between the upper spring seat Q of the coilspring and the vehicle body-side mounting member X to which a piston rodP is secured in a strut-type suspension assembly shown in FIG. 6, theinstallation operation is facilitated.

FIG. 9 shows the synthetic resin-made thrust sliding bearing 1 inaccordance with a third embodiment. In the synthetic resin-made thrustsliding bearing 1 in accordance with the third embodiment, the uppercasing 100 further has an annular projecting portion 109 a projecting inthe axial direction integrally from the upper surface 108 of the upperannular plate portion 102, the upper surface of the upper casing 100 isthe upper surface of the annular projecting portion 109 a, and theannular flat surface 109 is constituted by the upper surface of theannular projecting portion 109 a. If the length to the outer peripheralsurface 303 of the thrust bearing piece 300 disposed in the lowerannular recess 205 is assumed to be (r), the annular flat surface 109has an outer peripheral edge whose radius (R) with the axis (o) of theupper casing 100 set as a center is R=r, the annular projecting portion109 a being continuous from its outer peripheral surface to thetruncated conical surface portion 111 with a descending gradient. Theother arrangements of the synthetic resin-made thrust sliding bearing 1in accordance with this third embodiment are similar to those of thesynthetic resin-made thrust sliding bearing 1 in accordance with thefirst embodiment shown in FIG. 1. With the synthetic resin-made thrustsliding bearing 1 in accordance with such a third embodiment as well, ifthe thickness of the upper annular plate portion 102 at its innerperipheral surface is assumed to be (t), the annular flat surface 109,which is the upper surface of the upper casing 100, may have an outerperipheral edge with the radius (R) of R=r−t, or may have an outerperipheral edge with the radius (R) of R=r+t, i.e., may have an outerperipheral edge with the radius (R) in the range of R=r±t.

With the synthetic resin-made thrust sliding bearing 1 in accordancewith the third embodiment as well, the sum A of volumes of the innerannular clearances A1 and A2 and the volume B of that portion of thethrust bearing piece 300 which projects upward from the opening plane ofthe lower annular recess 205 are preferably in the relationship of B>A,i.e., e(b²−a²)>f(d²−c²).

According to the synthetic resin-made thrust sliding bearing 1 inaccordance with the third embodiment, it is possible to more reliablyavoid the interference at the radially superposed portions of thecylindrical suspended portion 104 and the annular projection 206 and thecylindrical engaging projecting portion 208 and at the resilientlyfitting portions of the engaging portion 107 of the cylindrical engagingsuspended portion 106 and the engaged portion 209 of the cylindricalengaging projecting portion 208 in the case where a fluctuating loadsuch as an inclination has acted on the vehicle body-side mountingmember X.

With the synthetic resin-made thrust sliding bearing 1 in accordancewith the third embodiment, in the same way as with the syntheticresin-made thrust sliding bearing 1 in accordance with the firstembodiment, sealed portions based on the labyrinth action are formed atthe radially superposed portions of the cylindrical suspended portion104 and the annular projection 206 and the cylindrical engagingprojecting portion 208 and at the resiliently fitting portions of theengaging portion 107 and the engaged portion 209. As a result, anoperational effect is added in that the entry of foreign objects such asdust between the upper and lower casings 100 and 200 can be prevented.

Also with the synthetic resin-made thrust sliding bearing 1 inaccordance with the third embodiment, in the same way as the thrustbearing pieces 300 of the synthetic resin-made thrust sliding bearings 1in accordance with the first and second embodiments, as shown in FIG. 2,the thrust bearing piece 300 should preferably have on each of its upperand lower surfaces 305 and 306 the annular groove 307 which surroundsthe circular hole 302, as well as the plurality of radial grooves 308each having one end open at the annular groove 307 and the other endopen at the outer peripheral surface 303 of the disk 304 and arranged atequal intervals in the circumferential direction. A lubricant such asgrease is filled in these annular grooves 307 and radial grooves 308.

Also with the synthetic resin-made thrust sliding bearing 1 inaccordance with the third embodiment, in the same way as the uppercasings 100, the lower casings 200, and the thrust bearing pieces 300 ofthe synthetic resin-made thrust sliding bearings 1 in accordance withthe first and second embodiments, as for the upper casing 100 and thelower casing 200, a thermoplastic synthetic resin such as polyacetalresin, polyamide resin, and polyester resin is suitably used, and as thesynthetic resin for forming the thrust bearing piece 300, athermoplastic synthetic resin such as polyamide resin, polyolefin resin,and polyester resin, which excel in the sliding characteristics withrespect to the thermoplastic synthetic resin for forming the uppercasing 100 and the lower casing 200, is suitably used.

FIG. 10 shows the synthetic resin-made thrust sliding bearing 1 inaccordance with a fourth embodiment. With this synthetic resin-madethrust sliding bearing 1, in the synthetic resin-made thrust slidingbearing 1 in accordance with the third embodiment, the upper casing 100further has a cylindrical suspended portion 114 which is radiallyoutwardly adjacent to the circular hole 101 in the central portion ofthe upper annular plate portion 102 via an annular shoulder portion 112,and is formed integrally on the lower surface 103 of the upper annularplate portion 102 in such a manner as to be radially inwardly spacedapart a predetermined interval from the inner peripheral surface of thecylindrical suspended portion 104, so as to form at its outer peripheralsurface an upper annular recess 113 in cooperation with the innerperipheral surface of the cylindrical suspended portion 104 and thelower surface 103 of the upper annular plate portion 102. The lowercasing 200 has an annular projection 216 which has an inside diameteridentical to that of the insertion hole 201 formed in the centralportion of the lower annular plate portion 202 and is formed integrallyon the upper surface 203 of the lower annular plate portion 202 in sucha manner as to be radially inwardly spaced apart a predeterminedinterval from the annular projection 204, so as to form at its outerperipheral surface a lower inner annular groove 215 in cooperation withthe inner peripheral surface of the annular projection 204. The uppercasing 100 is combined with the lower casing 200 by disposing the endportion of the cylindrical suspended portion 114 in the lower innerannular groove 215 so as to be radially superposed on the end portionsof the annular projections 204 and 216.

Also with the synthetic resin-made thrust sliding bearing 1 inaccordance with the fourth embodiment, in the same way as with thesynthetic resin-made thrust sliding bearing 1 in accordance with thethird embodiment, if the length to the outer peripheral surface 303 ofthe thrust bearing piece 300 disposed in the lower annular recess 205 isassumed to be (r), the annular flat surface 109 constituted by the uppersurface of the annular projecting portion 109 a has an outer peripheraledge whose radius (R) with the axis (o) of the upper casing 100 set as acenter is R=r, the annular projecting portion 109 a being continuousfrom its outer peripheral surface to the truncated conical surfaceportion 111 with a descending gradient. Also with the syntheticresin-made thrust sliding bearing 1 in accordance with this fourthembodiment, if the thickness of the upper annular plate portion 102 atits inner peripheral surface is assumed to be (t), the annular flatsurface 109, which is the upper surface of the upper casing 100, mayhave an outer peripheral edge with the radius (R) in the range of R=r±t.

According to the synthetic resin-made thrust sliding bearing 1 inaccordance with the fourth embodiment, it is possible to more reliablyavoid the interference at the radially superposed portions of thecylindrical suspended portion 104 and the annular projection 206 and thecylindrical engaging projecting portion 208 and at the resilientlyfitting portions of the engaging portion 107 and the engaged portion 209in the case where a fluctuating load such as an inclination has acted onthe vehicle body-side mounting member X.

With the synthetic resin-made thrust sliding bearing 1 in accordancewith the fourth embodiment as well, the sum A of volumes of the innerannular clearances A1 and A2 and the volume B of that portion of thethrust bearing piece 300 which projects upward from the opening plane ofthe lower annular recess 205 are preferably in the relationship of B>A,i.e., e(b²−a₂)>f(d²−c²).

With the synthetic resin-made thrust sliding bearing 1 in accordancewith the fourth embodiment, the upper casing 100 is combined with thelower casing 200 by disposing the end portion of the cylindricalsuspended portion 114 in the lower inner annular groove 215 so as to beradially superposed on the end portions of the annular projection 216and the annular projection 204, by disposing the end portion of thecylindrical suspended portion 104 in the lower outer annular groove 207so as to be radially superposed on the end portions of the annularprojection 206 and the cylindrical engaging projecting portion 208, andby causing the engaging portion 107 to be resiliently fitted to theengaged portion 209. Therefore, sealed portions based on the labyrinthaction are formed at the radially superposed portions of the cylindricalsuspended portion 114 and the annular projection 216 and the annularprojection 204, at the radially superposed portions of the cylindricalsuspended portion 104 and the annular projection 206 and cylindricalengaging projecting portion 208, and at the resiliently fitting portionsof the engaging portion 107 and the engaged portion 209. As a result, anoperational effect is added in that the entry of foreign objects such asdust between the upper and lower casings 100 and 200, particularly fromthe inner peripheral surface side of the upper and lower casings, isfurther prevented.

Also with the synthetic resin-made thrust sliding bearing 1 inaccordance with the fourth embodiment, in the same way as the thrustbearing piece 300 of the synthetic resin-made thrust sliding bearing 1in accordance with the first embodiment, as shown in FIG. 2, the thrustbearing piece 300 should preferably have on each of its upper and lowersurfaces 305 and 306 the annular groove 307 which surrounds the circularhole 302, as well as the plurality of radial grooves 308 each having oneend open at the annular groove 307 and the other end open at the outerperipheral surface 303 of the disk 304 and arranged at equal intervalsin the circumferential direction. A lubricant such as grease is filledin these annular grooves 307 and radial grooves 308.

Also with the synthetic resin-made thrust sliding bearing 1 inaccordance with the fourth embodiment, in the same way as the uppercasing 100, the lower casing 200, and the thrust bearing piece 300 ofthe synthetic resin-made thrust sliding bearing 1 in accordance with thefirst embodiment, as for the upper casing 100 and the lower casing 200,a thermoplastic synthetic resin such as polyacetal resin, polyamideresin, and polyester resin is suitably used, and as the synthetic resinfor forming the thrust bearing piece 300, a thermoplastic syntheticresin such as polyamide resin, polyolefin resin, and polyester resin,which excel in the sliding characteristics with respect to thethermoplastic synthetic resin for forming the upper casing 100 and thelower casing 200, is suitably used.

FIG. 11 shows the synthetic resin-made thrust sliding bearing 1 inaccordance with a fifth embodiment. With this synthetic resin-madethrust sliding bearing 1, in the synthetic resin-made thrust slidingbearing 1 in accordance with the third embodiment, the upper casing 100further has a cylindrical suspended portion 117 which has an insidediameter identical to that of the circular hole 201 in the centralportion of the upper annular plate portion 102 and is formed integrallyon the lower surface 103 of the upper annular plate portion 102, as wellas a cylindrical suspended portion 119 formed integrally on the lowersurface 103 of the upper annular plate portion 102 in such a manner asto be radially outwardly spaced apart a predetermined interval from theouter peripheral surface of the cylindrical suspended portion 117, so asto form at its inner peripheral surface an upper inner annular groove118 in cooperation with the outer peripheral surface of the cylindricalsuspended portion 117. The lower casing 200 further has an annularprojection 219 which is formed integrally on the upper surface 203 ofthe lower annular plate portion 202 in such a manner as to be radiallyoutwardly spaced apart from the insertion hole 201 in the centralportion of the lower annular plate portion 202 via an annular shoulderportion 217, and is disposed in such a manner as to be radially inwardlyspaced apart a predetermined interval from the inner peripheral surfaceof the annular projection 204, so as to form at its outer peripheralsurface a lower inner annular groove 218 in cooperation with the innerperipheral surface of the annular projection 204. The upper casing 100is combined with the lower casing 200 by radially superposing the endportion of the cylindrical suspended portion 117 on the end portion ofthe annular projection 219, by disposing the end portion of the annularprojection 219 in the upper inner annular groove 118, and by disposingthe end portion of the cylindrical suspended portion 119 in the lowerinner annular groove 218 so as to be radially superposed on the endportions of the annular projection 204 and the annular projection 219,respectively.

Also with the synthetic resin-made thrust sliding bearing 1 inaccordance with this fifth embodiment, in the same way as with thesynthetic resin-made thrust sliding bearings 1 in accordance with thethird and fourth embodiments, if the length to the outer peripheralsurface 303 of the thrust bearing piece 300 disposed in the lowerannular recess 205 is assumed to be (r), the annular flat surface 109constituted by the upper surface of the annular projecting portion 109 ahas an outer peripheral edge whose radius (R) with the axis (o) of theupper casing 100 set as a center is R=r, the annular projecting portion109 a being continuous from its outer peripheral surface to thetruncated conical surface portion 111 with a descending gradient. Alsowith the synthetic resin-made thrust sliding bearing 1 in accordancewith this fifth embodiment, if the thickness of the upper annular plateportion 102 at its inner peripheral surface is assumed to be (t), theannular flat surface 109, which is the upper surface of the upper casing100, may have an outer peripheral edge with the radius (R) in the rangeof R=r±t.

According to the synthetic resin-made thrust sliding bearing 1 inaccordance with the fifth embodiment, it is possible to more reliablyavoid the interference at the radially superposed portions of thecylindrical suspended portion 104 and the annular projection 206 and thecylindrical engaging projecting portion 208 and at the resilientlyfitting portions of the engaging portion 107 and the engaged portion 209in the case where a fluctuating load such as an inclination has acted onthe vehicle body-side mounting member X.

With the synthetic resin-made thrust sliding bearing 1 in accordancewith the fifth embodiment as well, the sum A of volumes of the innerannular clearances A1 and A2 and the volume B of that portion of thethrust bearing piece 300 which projects from the opening of the lowerannular recess 205 are preferably in the relationship of B>A, i.e.,e(b²−a²)>f(d²−c²).

With the synthetic resin-made thrust sliding bearing 1 in accordancewith the fifth embodiment, the upper casing 100 is combined with thelower casing 200 by radially superposing the end portion of thecylindrical suspended portion 117 on the end portion of the annularprojection 219, by disposing the end portion of the cylindricalsuspended portion 119 in the lower inner annular groove 218 so as to beradially superposed on the end portions of the annular projection 219and the annular projection 204, respectively, by disposing the endportion of the cylindrical suspended portion 104 in the lower outerannular groove 207 so as to be radially superposed on the end portionsof the annular projection 206 and the cylindrical engaging projectingportion 208, respectively, and by causing the engaging portion 107 to beresiliently fitted to the engaged portion 209. Therefore, sealedportions based on the labyrinth action are formed at the superposedportions of the cylindrical suspended portion 117 and the annularprojection 219, at the superposed portions of the cylindrical suspendedportion 119 and the annular projection 219 and the annular projection204, at the superposed portions of the cylindrical suspended portion 104and the annular projection 206 and the cylindrical engaging projectingportion 208, and at the resiliently fitting portions of the engagingportion 107 and the engaged portion 209. As a result, an operationaleffect is added in that the entry of foreign objects such as dustbetween the upper and lower casings 100 and 200, particularly from theinner peripheral surface side of the upper and lower casings, can befurther prevented.

Also with the synthetic resin-made thrust sliding bearing 1 inaccordance with the fifth embodiment, in the same way as the thrustbearing piece 300 of the synthetic resin-made thrust sliding bearing 1in accordance with the first embodiment, as shown in FIG. 2, the thrustbearing piece 300 should preferably have on each of its upper and lowersurfaces 305 and 306 the annular groove 307 which surrounds the circularhole 302, as well as the plurality of radial grooves 308 each having oneend open at the annular groove 307 and the other end open at the outerperipheral surface 303 of the disk 304 and arranged at equal intervalsin the circumferential direction. A lubricant such as grease is filledin these annular grooves 307 and radial grooves 308.

Also with the synthetic resin-made thrust sliding bearing 1 inaccordance with the fifth embodiment, in the same way as the uppercasings 100, the lower casings 200, and the thrust bearing pieces 300 ofthe synthetic resin-made thrust sliding bearings 1 in accordance withthe first to fourth embodiments, as for the upper casing 100 and thelower casing 200, a thermoplastic synthetic resin such as polyacetalresin, polyamide resin, and polyester resin is suitably used, and as thesynthetic resin for forming the thrust bearing piece 300, athermoplastic synthetic resin such as polyamide resin, polyolefin resin,and polyester resin, which excel in the sliding characteristics withrespect to the thermoplastic synthetic resin for forming the uppercasing 100 and the lower casing 200, is suitably used.

In the same way as the synthetic resin-made thrust sliding bearing 1 inaccordance with the second embodiment, each of the synthetic resin-madethrust sliding bearings 1 in accordance with the third, fourth, andfifth embodiments may have, in addition to the above-describedconstruction, the cylindrical portion 214 which has an inside diameteridentical to that of the insertion hole 201 and is formed integrallywith the lower surface 213 of the lower annular plate portion 202 of thelower casing 200.

As described above, in the synthetic resin-made thrust sliding bearingin accordance with the present invention, it is possible to morereliably avoid the interference at the radially superposed portions ofthe cylindrical suspended portion 104 and the annular projection 206 andthe cylindrical engaging projecting portion 208 and at the resilientlyfitting portions of the engaging portion 107 and the engaged portion 209even in the case where a fluctuating load such as an inclination hasacted on the vehicle body-side mounting member.

In the synthetic resin-made thrust sliding bearing in accordance withthe invention in which the sum A of the volumes of the inner annularclearance A1 and the outer annular clearance A2 and the volume B of thatportion of the thrust bearing piece which projects upward from theopening plane of the lower annular recess are in the relationship ofB>A, i.e., e(b²−a²)>f(d²−c²), even in cases where a change (decrease) inthe thickness due to creep deformation has occurred to the thrustbearing piece in the lower annular recess, the change (decrease) in thethickness is restrained in the lower annular recess, and its furtherchange (decrease) in the thickness is prevented. Further, since theupper surface of the thrust bearing piece constantly projects from theopening plane of the lower annular recess of the lower casing, the upperand lower casings can constantly be made to undergo sliding through thethrust bearing piece without shifting to sliding between the upper andlower casings. Thus, an operational effect is added in that it ispossible to maintain the sliding characteristics such as low frictioncharacteristics and wear resistance for extended periods of time.

The invention claimed is:
 1. A synthetic resin-made thrust slidingbearing comprising: a synthetic resin-made upper casing including anupper annular plate portion having a circular hole in its centralportion; a synthetic resin-made lower casing including a lower annularplate portion having in its central portion an insertion hole concentricwith the circular hole of said upper annular plate portion; and a thrustbearing piece formed in a form of a synthetic resin-made annular diskand having a circular hole in a central portion thereof, wherein if itis assumed that a radial length from an axis of said upper casing to theouter peripheral surface of said thrust bearing piece is (r), and athickness of said upper annular plate portion at its inner peripheralsurface is (t), said upper casing has on its upper surface an annularflat surface having a circular outer peripheral edge whose radius (R)with the axis of said upper casing set as a center is in a range ofR=r−t.
 2. The synthetic resin-made thrust sliding bearing according toclaim 1, wherein the upper surface of said upper casing is an uppersurface of said upper annular plate portion.
 3. The synthetic resin-madethrust sliding bearing according to claim 1, wherein said upper casingfurther has an annular projecting portion projecting in an axialdirection integrally from an upper surface of said upper annular plateportion, the upper surface of said upper casing is an upper surface ofsaid annular projecting portion, and the annular flat surface isconstituted by the upper surface of said annular projecting portion. 4.The synthetic resin-made thrust sliding bearing according to claim 1,wherein said upper casing has on its upper surface a truncated conicalsurface portion with a descending gradient extending from an outerperipheral edge of the annular flat surface or from a radially outerportion of that outer peripheral edge to its outer peripheral surface.5. The synthetic resin-made thrust sliding bearing according to claim 1,wherein said thrust bearing piece has on each of an upper surface and alower surface thereof an annular groove which surrounds the circularhole and a plurality of radial grooves each having one end open at theannular groove and another end open at the outer peripheral surface andarranged in a circumferential direction.
 6. The synthetic resin-madethrust sliding bearing according to claim 1, wherein said lower casinghas a cylindrical portion formed integrally on the lower surface of saidlower annular plate portion and having an inside diameter identical tothat of the insertion hole.